Package org.apache.lucene.util.fst

Class FSTCompiler<T>

java.lang.Object
org.apache.lucene.util.fst.FSTCompiler<T>
public class FSTCompiler<T> extends Object
Builds a minimal FST (maps an IntsRef term to an arbitrary output) from pre-sorted terms with outputs. The FST becomes an FSA if you use NoOutputs. The FST is written on-the-fly into a compact serialized format byte array, which can be saved to / loaded from a Directory or used directly for traversal. The FST is always finite (no cycles).

NOTE: The algorithm is described at http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.24.3698

The parameterized type T is the output type. See the subclasses of Outputs.

FSTs larger than 2.1GB are now possible (as of Lucene 4.2). FSTs containing more than 2.1B nodes are also now possible, however they cannot be packed.

WARNING: This API is experimental and might change in incompatible ways in the next release.

  • Constructor Details

    • FSTCompiler

      public FSTCompiler(FST.INPUT_TYPE inputType, Outputs<T> outputs)
      Instantiates an FST/FSA builder with default settings and pruning options turned off. For more tuning and tweaking, see FSTCompiler.Builder.

  • Method Details

    • getDirectAddressingMaxOversizingFactor

      public float getDirectAddressingMaxOversizingFactor()

    • getTermCount

      public long getTermCount()

    • getNodeCount

      public long getNodeCount()

    • getArcCount

      public long getArcCount()

    • getMappedStateCount

      public long getMappedStateCount()

    • add

      public void add(IntsRef input, T output) throws IOException
      Add the next input/output pair. The provided input must be sorted after the previous one according to IntsRef.compareTo(org.apache.lucene.util.IntsRef). It's also OK to add the same input twice in a row with different outputs, as long as Outputs implements the Outputs.merge(T, T) method. Note that input is fully consumed after this method is returned (so caller is free to reuse), but output is not. So if your outputs are changeable (eg ByteSequenceOutputs or IntSequenceOutputs) then you cannot reuse across calls.
      Throws:
      IOException

    • compile

      public FST<T> compile() throws IOException
      Returns final FST. NOTE: this will return null if nothing is accepted by the FST.
      Throws:
      IOException

    • fstRamBytesUsed

      public long fstRamBytesUsed()